Crosslinkable macromers

ABSTRACT

A crosslinkable macromer system and related methods of preparing the system and using the system in the form of a crosslinked matrix between a tissue site and an implant article such as a tissue implant or on the porous surface of a prosthetic device. The macromer system includes two or more polymer-pendent polymerizable groups and one or more initiator groups (e.g., polymer-pendent initiator groups). The polymerizable groups and the initiator group(s), when polymer-pendent, can be pendent on the same or different polymeric backbones. The macromer system provides advantages over the use of polymerizable macromers and separate, low molecular weight initiators, including advantages with respect to such properties as nontoxicity, efficiency, and solubility. A macromer system of the invention can be used as an interface between the tissue site and implant article in a manner sufficient to permit tissue growth through the crosslinked matrix and between the tissue site and implant. In a preferred embodiment, polymers with pendent polymerizable groups, for use in the macromer system, are prepared by reacting a polysaccharide polymer with a reactive moiety in an organic, polar solvent such as formamide.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of U.S. Ser. No.09/571,525, filed May 16, 2000, which is a continuation -in-part of U.S.Ser. No. 09/469,976, filed Dec. 21, 1999, which is a divisional of USpatent application filed Jul. 23, 1998 and assigned Ser. No. 09/121,248(now U.S. Pat. No. 6,007,833), which is a continuation of provisional USpatent application filed Mar. 19, 1998 and assigned Serial No.60/078,607, the entire disclosures of which are incorporated herein byreference.

TECHNICAL FIELD

[0002] The present invention relates to the preparation of matrices bythe polymerization of macromers. In another aspect, the inventionrelates to the use of such matrices for such purposes as cellimmobilization, tissue adherence, and controlled drug delivery.

BACKGROUND OF THE INVENTION

[0003] Matrices are polymeric networks characterized by insolubility inwater. One type of polymeric matrix is a hydrogel, which can be definedas a water-containing polymeric network. The polymers used to preparehydrogels can be based on a variety of monomer types, such as thosebased on methacrylic and acrylic ester monomers, acrylamide(methacrylamide) monomers, and N-vinyl-2-pyrrolidone. To form the gel,these monomer classes are typically crosslinked with such crosslinkingagents as ethylene dimethacrylate, N,N′-methylenebisacrylamide,methylenebis(4-phenyl isocyanate), ethylene dimethacrylate,divinylbenzene, and allyl methacrylate.

[0004] Another type of polymeric network can be formed from morehydrophobic monomers and/or macromers. Matrices formed from thesematerials generally exclude water. Polymers used to prepare hydrophobicmatrices can be based on a variety of monomer types such as alkylacrylates and methacrylates, and polyester-forming monomers such asε-caprolactone and lactide. When formulated for use in an aqueousenvironment, these materials do not need to be crosslinked, but they canbe crosslinked with standard agents such as divinyl benzene. Hydrophobicmatrices can also be formed from reactions of macromers bearing theappropriate reactive groups such as the reaction of diisocyanatemacromers with dihydroxy macromers, and the reaction ofdiepoxy-containing macromers with dianhydride or diamine-containingmacromers.

[0005] Although there exist a variety of methods for producing polymericnetworks, when these networks are intended to be created in the presenceof viable tissue, and/or to contain a bioactive compound, the number ofacceptable methods of producing polymeric networks is extremely limited.

[0006] It is nevertheless desirable to form both hydrogel andnon-hydrogel polymeric matrices in the presence of viable tissue orbioactive agents for the purposes of drug delivery, cellular immuneisolation, prevention of post-surgical adhesions, tissue repair, and thelike. These polymeric matrices can be divided into two categories:biodegradable or bioresorbable polymer networks and biostable polymernetworks.

[0007] Biodegradable polymeric matrices have been previously suggestedfor a variety of purposes, including controlled release carriers,adhesives and sealers. When used as controlled release carriers, forinstance, polymeric matrices can contain and release drugs or othertherapeutic agents over time. Such matrices can be formed, for instance,by a number of different processes, including solvent castinghydrophobic polymers. Solvent casting, however, typically involves theuse of organic solvents and/or high temperatures which can bedetrimental to the activity of biological materials and can complicateproduction methods. Solvent casting of polymers out of solution alsoresults in the formation of uncrosslinked matrices. Such matrices haveless structure than crosslinked matrices and it is more difficult tocontrol the release of bioactive agents from such matrices. Yet anotherprocess, which involves the polymerization of monomers in or around thedesired materials, suffers from cytotoxicity of monomers, oxygeninhibition and heat of polymerization complications.

[0008] Another process used in the past to prepare biodegradable andbiostable hydrogels involves the polymerization of preformed macromersusing low molecular weight initiators. This process involves a number ofdrawbacks as well, however, including toxicity, efficacy, and solubilityconsiderations. For instance, when using a macromer solution containinga low molecular weight soluble initiator to encapsulate viable cellularmaterial, the initiator can penetrate the cellular membrane and diffuseinto the cells. The presence of the initiator may involve some toxicconsequence to the cells. When activated, however, these initiatorsproduce free radicals having distinct cytotoxic potential. Otherdrawbacks arise if the initiator is able to diffuse out of the formedmatrix, thereby producing toxicity and other issues. Such initiatorsalso tend to aggregate in aqueous solution, causing efficiency andreproducibility problems. Finally, in view of the limited efficiency ofmany initiators for initiating the necessary radical chainpolymerization, it is often necessary to add one or more monomericpolymerization “accelerators” to the polymerization mixture. Suchaccelerators tend to be small molecules capable of penetrating thecellular membrane, and often raise cytotoxic or carcinogenic concerns.

[0009] U.S. Pat. Nos. 5,410,016 (Hubbell, et al.) and 5,529,914(Hubbell, et.al.) for instance, relate to hydrogels prepared frombiodegradable and biostable polymerizable macromers. The hydrogels areprepared from these polymerizable macromers by the use of soluble, lowmolecular weight initiators. Such initiators can be combined with themacromers, and irradiated in the presence of cells, in order to form agel that encapsulates the cells. A considerable number of similar andrelated patents have arisen over recent years. See, for instance, U.S.Pat. Nos. 5,232,984; 5,380,536; 5,573,934; 5,612,050; 5,837,747;5,846,530; and 5,858,746.

[0010] Hydrogels often suffer from similar or other drawbacks in use asbiological adhesives or sealants, e.g., for use as tissue adhesives,endovascular paving, prevention of post-surgical adhesions, etc. In eachof the applications, the hydrogel matrix must generally “adhere” to oneor more tissue surfaces. Current methods rely upon physical “adhesion”or the tendency of hydrogels to “stick” to a surface. A superioradhesive would provide both physical and chemical adhesion to surfacesutilizing the same physical characteristics as current hydrogeladhesives, but also providing chemical, covalent coupling of the matrixmaterial to the tissue surface. Covalent bonds are generally muchstronger than physical adhesive forces, such as hydrogen bonding and vander Waals forces.

[0011] As described above, when various techniques are used to formpolymeric matrices via photoinitiation of macromers, the photoinitiatorsutilized tend to be low molecular weight. Polymeric photoinitiators havebeen described as well, although for applications and systems quitedistinct from those described above. See, for instance, “RadicalPolymerization”, C. H. Bamford, pp. 940-957 in Kroschwitz, ed., ConciseEncyclopedia of Polymer Science and Engineering, 1990. In the subsectionentitled “Photosensitized Initiation: Polymeric Photosensitizers andPhotoinitiators”, the author states that “[p]olymeric photosensitizersand photoinitiators have been described. Many of these are polymersbased on benzophenone, e.g., poly(p-divinylbenzophenone) (DVBP). Suchrigid polymers are reported to be effective sensitizers since hydrogenabstraction from the backbone by excited benzophenone is less likely.”

[0012] U.S. Pat. No. 4,315,998 (Neckers) describes polymer-boundphotosensitizing catalysts for use in the heterogeneous catalysis ofphotosensitized chemical reactions such as photo-oxidation,photodimerization, and photocyclo addition reactions. The polymer-boundphotosensitizing catalysts are insoluble in water and common organicsolvents, and therefore can be readily separated from the reactionmedium and reaction products by simple filtration.

[0013] What is clearly needed are macromers and macromer systems thatavoid the problems associated with conventional polymeric matrices, andin particular, those drawbacks that arise when polymeric matrices areformed in the presence of viable tissue or bioactive agents.

SUMMARY OF THE INVENTION

[0014] The present invention provides a method of improving theperformance, within a host tissue site, of an implanted article (e.g.,implanted tissue or implanted prosthetic device providing a poroussurface), by promoting the growth of continuous tissue between hosttissue and the implant. An implanted article of this invention can beprovided, for instance, in the form of cultured tissue and/or nativetissue (e.g., transplanted tissue), or can be fabricated from polymericand/or metallic materials. The method employs a crosslinkable macromersystem adapted to form an interface between the article and the hosttissue, in order to facilitate (e.g., promote and/or permit) tissueintegration by the body between the implant and the tissue site, e.g.,into and through the crosslinked macromer and into the porosity of aporous device surface.

[0015] Applicant's parent application Ser. No. 09/121,248 (now U.S. Pat.No. 6,007,833) provides examples of preferred macromer systems useful inthe method of the present invention. The parent application teaches theuse of such systems for various applications, including cellularencapsulation, adhesives and sealants, barriers, controlled releasecarriers, tissue replacement/scaffolding, wound dressings, and in situdevice formation. For use in tissue replacement, for instance, theparent application teaches the placement of a macromer system in a moldor cavities in a device.

[0016] Polymeric matrices of this invention (as formed by crosslinkingthe macromer system) can be used, for instance, to improve the tissueresponse to implanted medical devices. Examples of improved tissueresponse include: 1) increased tissue ingrowth (e.g., into the pores ofcementless hip implants), and, 2) decreased fibrosis (e.g., aroundbreast implants and hernia repair meshes). In addition to tissueintegration, the macromer system can provide a variety of advantages,including a reduction in both immediate and chronic adverse reactions tothe device (e.g., thereby preventing the accumulation of fluid and/orundesirable cells) by virtue of the immediate and desirable spacefilling characteristics.

[0017] A macromer system of this invention can be provided between theimplant and tissue site in any suitable manner, e.g., the system can beprovided upon the surface of the implant before, during and/or afterplacement of the implant in the tissue site. Similarly, the macromersystem(s) can be polymerized to form a matrix at any suitable point,e.g., a system can be coated on an implant, and/or delivered to thetissue site, and crosslinked either before, during and/or afterpositioning the implant in or upon the tissue site. For example, asystem can be provided and crosslinked on the surface of a prostheticdevice, e.g., by either the manufacturer or surgeon, and implanted intothe tissue site. As another example, a macromer system can be applied tothe tissue site itself, polymerized in situ (e.g., by the application ofillumination either directly to the system or through translucenttissue), and an implant article (with or without a macromer system ormatrix on its surface) positioned on or in the site.

[0018] The resulting combination of implant and matrix within the tissuesite, permits the formation of continuous tissue growth, over time,through the matrix and between the implant and tissue site. Such growthcan be unidirectional (e.g., originating from the tissue site toward theimplant) and/or bidirectional (e.g., originating from both the tissuesite and from an implanted tissue).

[0019] A system, or resultant matrix, can be applied with or withoutadditional components, such as growth factors, morphogenic factors, orDNA. Both degradable and non-degradable macromer systems are useful, butmatrices adapted to degrade with desired kinetics, are preferred.

[0020] In another aspect, the present invention provides a combinationcomprising an implant article, such as a tissue implant or prostheticdevice having one or more porous surfaces, and a matrix formed of acrosslinked macromer system as described herein. In one embodiment, thearticle and uncrosslinked macromer system are initially combined (e.g.,the system coated on the article) outside the body, thereby permittingthe system to be crosslinked prior to, during and/or following placementof the implant within the body site. In an alternative embodiment, thecombination is provided by positioning an article within and/or inapposition to the body site, and delivering the macromer system to thebody site (before, during and/or after placement of the article itself),where it is crosslinked as a sufficiently stable coating or othersuitable interface in its position between the article and the tissuesite.

[0021] For instance, a macromer system in liquid (e.g., substantiallyflowable) form can be applied to a tissue defect, before, during orafter which a tissue implant or preformed device is pressed into thedefect. The system can be provided, for instance, to occupy a space ofbetween about 0.1 mm to about 10 mm between the implant and the tissuesite. The system is illuminated in order to activate the initiatorgroups and thus polymerize the macromer system into a solid matrix. Theresultant combination of tissue implant or preformed device, togetherwith crosslinked macromer system, completely and conformally fills thedefect such that no gaps remain for the accumulation of undesirablefluids or cells.

[0022] As described herein, the macromer system can thus be used in themanner of a “grout”, for instance, to fill the spaces between a tissueimplant or preformed device (itself either tissue-based or non-tissuebased) and adjacent tissue. Current tissue implants include, forinstance, both those obtained as transplants (e.g., autografts,allografts or xenografts) and those provided by tissue engineering.Current tissue engineering products often consist of cultured tissuesthat are implanted into tissue defects. Such products do not typicallyconform well to adjacent native tissue, however, thus leaving spacesinto which undesirable fluids and cells can accumulate and produceadverse tissue responses. For example, when cultured cartilage isimplanted into cartilage defects, synovial fluid and macrophages canenter the unfilled space and lead to fibrous tissue formation, whichprevents integration of the implanted cartilage with the nativecartilage. Other cultured tissues that are implanted into tissuedefects, and that would benefit from the present macromer system appliedas a grout include, but are not limited to, skin, bone, ligaments, bloodvessels, and heart valves.

[0023] Implants, e.g., prosthetic devices, useful in a combination ormethod of this invention include those in which tissue integration isdesired, and that themselves provide (or can be provided with) asufficiently porous surface that permits or facilitates tissueintegration once positioned in vivo. Examples of suitable porousprosthetic devices include, but are not limited to; joint implants(e.g., for hip or knee reconstruction), dental implants, soft tissuecosmetic prostheses (e.g., breast implants), wound dressings, vascularprostheses (e.g., vascular grafts and stents), and ophthalmic prostheses(e.g., intracorneal lenses). The macromer system of this invention, inturn, can be used in any suitable manner, e.g., to coat and/or fillvoids within or upon the surface of the prosthetic device.

[0024] Such devices preferably are themselves formed of or otherwiseprovide (or can be provided with) a surface having sufficient porosityto permit tissue ingrowth in vivo. As used herein, the word “porous”,and inflections thereof, will refer to one or more portions of thedevice surface that are designed for direct or indirect contact with thesurrounding natural tissue, sufficient to permit tissue integration intothe porosity thereof. Porous surfaces can be provided in a variety ofways, e.g., as sintered particles on a surface, such as titaniumparticles on the surface of cementless hip implants, as are availablefrom a variety of orthopedic companies. Porous surfaces can also beprovided in the form of cavities that remain from mixing salt crystalswith silicone rubber oligomers, then solidifying (vulcanizing) thesilicone rubber, and finally dissolving the salt crystals (as currentlydone for a variety of breast implants). Yet other porous surfaces can befabricated from fibrous materials or produced as porous sponges viasolvent casting and particulate leaching, phase separation, or gasfoaming (see, e.g., B. S. Kim and D. J. Mooney, Development ofBiocompatible Synthetic Extracellular Matricies for Tissue EngineeringTIBTECH 16:224-230 (1998).

[0025] Such porous surfaces typically provide a three-dimensionalstructure of spaces into which tissue can grow and mature. Porousregions of an implantable device preferably have a high pore density, inthat the pores themselves occupy a greater relative volume than thematerial forming and separating those pores. Desirably, the pores haveinterconnected passages that allow direct contact between the tissuegrowing in adjacent pores. The minimum average pore size is preferablysufficient to accommodate capillaries (e.g., of about 5 micron diameter)and the maximum average pore size is about 1 mm. Preferable pore sizeswill vary from tissue to tissue and typically range from about 20microns to about 600 microns, and more preferably from about 50 micronsto about 400 microns.

[0026] A crosslinkable macromer system useful in the present inventioncomprises two or more polymer-pendent polymerizable groups and one ormore initiators, preferably in the form of polymer-pendent initiatorgroups. In a preferred embodiment, the polymerizable groups and theinitiator group(s) are pendent on the same polymeric backbone. In analternative preferred embodiment, the polymerizable groups and initiatorgroup(s) are pendent on different polymeric backbones.

[0027] In the first embodiment, the macromer system comprises apolymeric backbone to which are covalently bonded both the polymerizablegroups and initiator group(s). Pendent initiator groups can be providedby bonding the groups to the backbone at any suitable time, e.g., eitherprior to the formation of the macromer (for instance, to monomers usedto prepare the macromer), or to the fully formed macromer itself. Themacromer system itself will typically comprise but a small percentage ofmacromers bearing both initiator groups and polymerizable groups. Themajority of macromers will provide only pendent polymerizable groups,since the initiator groups are typically sufficient if present at farless than 1:1 stoichiometric ratio with macromer molecules.

[0028] In an alternative preferred embodiment, the macromer systemcomprises both polymerizable macromers, generally without pendentinitiator groups, in combination with a polymeric initiator. In eitherembodiment, the initiator will be referred to herein as a “polymericinitiator”, by virtue of the attachment of such initiator groups to apolymeric backbone. Yet another embodiment of this invention includesthe macromer system having free (non-polymer bound) initiator molecules.

[0029] Macromer systems of the present invention, employing polymericinitiators, provide a number of unexpected advantages over the use ofpolymerizable macromers and separate, low molecular weight initiators.Such systems, for instance, provide an optimal combination of suchproperties as nontoxicity, efficiency, and solubility. Solubility, forinstance, can be improved by virtue of the ability to control theaqueous or organic solubility of the polymerizable macromer bycontrolling the backbone. Toxicity can also be improved, since thepolymeric initiators of this invention typically cannot diffuse intocells in the course of immobilization.

[0030] In a preferred embodiment, the pendent initiator groups areselected from the group consisting of long-wave ultra violet (LWUV)light-activatable molecules such as; 4-benzoylbenzoic acid,[(9-oxo-2-thioxanthanyl)-oxy]acetic acid, 2-hydroxy thioxanthone, andvinyloxymethylbenzoin methyl ether; visible light activatable molecules;eosin Y, rose bengal, camphorquinone and erythrosin, and thermallyactivatable molecules; 4,4′ azobis(4-cyanopentanoic) acid and2,2-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride. An importantcharacteristic of the initiator group being the ability to be coupled toa preformed macromer containing polymerizable groups, or to be modifiedto form a monomer which can take part in the macromer synthesis, whichis subsequently followed by the addition of polymerizable groups.

[0031] In such an embodiment, the pendent polymerizable groups arepreferably selected from the group consisting of pendent vinyl groups,acrylate groups, methacrylate groups, ethacrylate groups, 2-phenylacrylate groups, acrylamide groups, methacrylamide groups, itaconategroups, and styrene groups.

[0032] In a further preferred embodiment, the polymeric backbone isselected from the group consisting of synthetic macromers, such aspolyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyethyleneglycol (PEG); derivatizable naturally occurring polymers such ascellulose; polysaccharides, such as hyaluronic acid, dextran, andheparin; and proteins, such as collagen, gelatin, and albumin.

[0033] The macromers of the present invention can be used in a varietyof applications, including controlled drug release, the preparation oftissue adhesives and sealants, the immobilization of cells, and thepreparation of three-dimensional bodies for implants. In one aspect, forinstance, the invention provides a method for immobilizing cells, themethod comprising the steps of combining a polymeric initiator of thepresent invention with one or more polymerizable macromers and in thepresence of cells, under conditions suitable to polymerize the macromerin a manner that immobilizes the cells.

DETAILED DESCRIPTION

[0034] As used herein the following words and terms shall have themeaning ascribed below:

[0035] “macromer system” shall refer to a polymerizable polymer systemcomprising one or more polymers providing pendent polymerizable andinitiator groups. Groups can be present either on the same or differentpolymeric backbones, e.g., on either a polymerizable macromer or anon-polymerizable polymeric backbone;

[0036] “polymerizable macromer” shall refer to a polymeric backbonebearing two or more polymerizable (e.g., vinyl) groups;

[0037] “initiator group” shall refer to a chemical group capable ofinitiating a free radical reaction, present as either a pendent group ona polymerizable macromer or pendent on a separate, non-polymerizablepolymer backbone; and

[0038] “polymeric initiator” shall refer to a polymeric backbone(polymerizable or non-polymerizable) comprising one or more initiatorgroups and optionally containing one or more other thermochemicallyreactive groups or affinity groups.

[0039] The polymeric backbone of this invention can be either syntheticor naturally-occurring, and includes a number of macromers previouslydescribed as useful for the preparation of polymeric matrices.Generally, the backbone is one that is soluble, or nearly soluble, inaqueous solutions such as water, or water with added organic solvent(e.g., dimethylsulfoxide) or can be rendered soluble using anappropriate solvent or combination of solvents. Alternatively, thepolymeric backbone can be a material which is a liquid under ambientphysiological conditions. Backbones for use in preparing biodegradablegels are preferably hydrolyzable under in vivo conditions.

[0040] In general, the polymeric backbones of this invention can bedivided into two categories: biodegradable or bioresorbable, andbiostable reagents. These can be further divided into reagents whichform hydrophilic, hydrogel matricies and reagents which formnon-hydrogel matricies.

[0041] Bioresorbable hydrogel-forming backbones are generally naturallyoccurring polymers such as polysaccharides, examples of which include,but are not limited to, hyaluronic acid (HA), starch, dextran, heparin,chondroitin sulfate, dermatan sulfate, heparan sulfate, keratan sulfate,dextran sulfate, pentosan polysulfate, and chitosan; and proteins (andother polyamino acids), examples of which include but are not limited togelatin, collagen, fibronectin, laminin, albumin, elastin, and activepeptide domains thereof. Matrices formed from these materials degradeunder physiological conditions, generally via enzyme-mediatedhydrolysis.

[0042] Hyaluronic acid, when derivatized with polymerizable groups inthe manner described herein, provides a variety of advantages andbenefits not heretofore known or achievable. Hyaluronic acid hasconventionally been derivatized in aqueous conditions (see, e.g.,Soon-Shiong (U.S. Pat. No. 5,837,747), Sakurai (U.S. Pat. No.4,716,224), and Matsuda (U.S. Pat. No. 5,763,504). Occasional referenceshave described the ability to derivatize hyaluronic acid under organicconditions (see, e.g., Della Valle, U.S. Pat. No. 5,676,964). In most,if not all, such approaches, however, the reaction mixtures are eithersuspensions, as opposed to true solutions, or the hyaluronic acid isitself pre-reacted (typically in a predominantly aqueous mixture) toenhance its solubility in organic solvents.

[0043] Applicants have discovered the manner in which hyaluronic acid,as well as other polysaccharides and polyamino acids (such as collagen)can be effectively derivatized in organic, polar, anhydrous solvents andsolvent combinations. A particularly preferred solvent is formamide, andcombinations of other solvents therewith. Functionally, the solvent orsolvent system is one in which the polymer is sufficiently soluble andthat permits its derivatization to the desired extent. The ability toderivatize such polymers in the manner of this invention provides avariety of unexpected benefits, and an optimal combination of suchproperties as preparation cost, controllability, and yield.

[0044] As exemplifed below, for instance, hyaluronic acid is reacted informamide (and TEA, for pH control) with a reactive moiety in the formof glycidyl acrylate in order to derivatize the hyaluronic acidmolecules with acrylate groups. The number and/or density of acrylategroups can be controlled using the present method, e.g., by controllingthe relative concentration of reactive moiety to saccharide groupcontent.

[0045] Bioresorbable matrix-forming backbones are generally syntheticpolymers prepared via condensation polymerization of one or moremonomers. Matrix-forming polymers of this type include polylactide(PLA), polyglycolide (PGA), polycaprolactone (PCL), as well ascopolymers of these materials, polyanhydrides, and polyortho esters.

[0046] Biostable hydrogel matrix-forming backbones are generallysynthetic or naturally occurring polymers which are soluble in water,matrices of which are hydrogels or water-containing gels. Examples ofthis type of backbone include polyvinylpyrrolidone (PVP), polyethyleneglycol (PEG), polyacrylamide (PAA), polyvinyl alcohol (PVA), and thelike.

[0047] Biostable matrix-forming backbones are generally syntheticpolymers formed from hydrophobic monomers such as methyl methacrylate,butyl methacrylate, dimethyl siloxanes, and the like. These backbonematerials generally do not possess significant water solubility but canbe formulated as neat liquids which form strong matrices uponactivation. It is also possible to synthesize backbone polymers whichcontain both hydrophilic and hydrophobic monomers.

[0048] Polymeric backbones of polymerizable macromers can optionallyprovide a number of desirable functions or attributes, e.g., asdescribed in the above-captioned Hubbell patents, the disclosures ofwhich are incorporated herein by reference. Backbones can be providedwith water soluble regions, biodegradable regions, hydrophobic regions,as well as polymerizable regions.

[0049] As used herein, the term “polymerizable group” will generallyrefer to a group that is polymerizable by initiation by free radicalgeneration, most preferably by photoinitiators activated by visible orlong wavelength ultraviolet radiation. Preferred polymerizable groupsinclude acrylates, methacrylates, ethacrylates, itaconates, acrylamides,methacrylamide, and styrene.

[0050] Typically, polymerizable groups are incorporated into a macromersubsequent to the initial macromer formation using standardthermochemical reactions. Thus, for example, polymerizable groups can beadded to collagen via reaction of amine containing lysine residues withacryloyl chloride or glycidyl acrylate. These reactions result incollagen containing pendent polymerizable moieties. Similarly, whensynthesizing a macromer for use as described in the present invention,monomers containing reactive groups can be incorporated into thesynthetic scheme. For example, hydroxyethylmethacrylate (HEMA) oraminopropylmethacrylamide (APMA) can be copolymerized withN-vinylpyrrolidone or acrylamide yielding a water-soluble polymer withpendent hydroxyl or amine groups. These pendent groups can subsequentlybe reacted with acryloyl chloride or glycidyl acrylate to formwater-soluble polymers with pendent polymerizable groups.

[0051] Initiator groups useful in the system of the present inventioninclude those that can be used to initiate, by free radical generation,polymerization of the macromers to a desired extent and within a desiredtime frame. Crosslinking and polymerization are generally initiatedamong macromers by a light-activated free-radical polymerizationinitiator. Preferred initiators for long wave UV and visible lightinitiation include ethyl eosin, 2,2-dimethoxy-2-phenyl acetophenone,other acetophenone derivatives, thioxanthone, benzophenone, andcamphorquinone.

[0052] Preferred polymeric initiators are photosensitive molecules whichcapture light energy and initiate polymerization of the macromers. Otherpreferred polymeric initiators are thermosensitive molecules whichcapture thermal energy and initiate polymerization of the macromers.

[0053] Photoinitiation of the free radical polymerization of macromersof the present invention will generally occur by one of threemechanisms. The first mechanism involves a homolytic alpha cleavagereaction between a carbonyl group and an adjacent carbon atom. This typeof reaction is generally referred to as a Norrish type I reaction.Examples of molecules exhibiting Norrish type I reactivity and useful ina polymeric initiating system include derivatives of benzoin ether andacetophenone.

[0054] The second mechanism involves a hydrogen abstraction reaction,either intra- or intermolecular. This initiation system can be usedwithout additional energy transfer acceptor molecules and utilizingnonspecific hydrogen abstraction, but is more commonly used with anenergy transfer acceptor, typically a tertiary amine, which results inthe formation of both aminoalkyl radicals and ketyl radicals. Examplesof molecules exhibiting hydrogen abstraction reactivity and useful in apolymeric initiating system, include analogs of benzophenone,thioxanthone, and camphorquinone.

[0055] When using a polymeric initiator of the hydrogen abstractionvariety, pendent tertiary amine groups can be incorporated into thepolymeric backbone of the macromer. This will insure that all freeradicals formed are polymer-bound.

[0056] The third mechanism involves photosensitization reactionsutilizing photoreducible or photo-oxidizable dyes. In most instances,photoreducible dyes are used in conjunction with a reductant, typically,a tertiary amine. The reductant intercepts the induced triplet producingthe radical anion of the dye and the radical cation of the reductant.Examples of molecules exhibiting photosensitization reactivity anduseful in a polymeric initiating system include eosin Y, rose bengal,and erythrosin. Reductants can be incorporated into the polymerbackbone, thereby assuring that all free radicals will be polymer-bound.

[0057] Thermally reactive polymeric initiators are also useful for thepolymerization of macromers. Examples of thermally reactive initiatorsusable in a polymeric initiating system include 4,4′azobis(4-cyanopentanoic acid) and analogs of benzoyl peroxide.

[0058] A surprisingly beneficial effect of the use of polymericinitiators to polymerize macromers is the increased efficiency ofpolymerization exhibited by these polymeric initiators as compared totheir low molecular weight counterparts. This increased efficiency isseen in all three photoinitiation mechanisms useful for thepolymerization of macromers.

[0059] Polymeric initiation of monomer solutions has been investigatedfor its application in the field of UV-curable coatings for industrialuses, c.f. U.S. Pat. No. 4,315,998 (Neckers) and PCT Application,International Publication No. WO 97/24376 (Kuester, et.al.) but therehave been no reports of the adaptation of the use of polymericinitiators for the polymerization of macromers in the presence ofbiologic material or for the creation of drug-releasing matrices.

[0060] High efficiency of initiation is particularly important insystems such as these. It is generally desirable, when forming polymericmatrices in the presence of biologic or bioactive materials, to minimizethe exposure time of the material to the energy source used to initiatepolymerization. It is therefore imperative that the initiation systemutilized possess optimum initiation efficiency.

[0061] When matrix strength or durability are required for a particularapplication, high efficiency is again a necessary characteristic of aninitiation system. When a matrix-forming system is initiated, the freeradical polymerization of the system is propagated until gelation andvitrification of the polymerizing system render the diffusion of theelements of the matrix-forming system too difficult. Therefore, thehigher the efficiency of the initiation system, the more complete thepolymerization resulting in the formation of stronger, more durablematrices. The polymeric initiation systems described in this inventionprovide a higher degree of efficiency, with or without the use ofaccelerants, than is attainable using nonpolymer-bound, low molecularweight initiators.

[0062] Another beneficial effect is realized when the initiating groupson the polymeric initiators consist of groups exhibiting hydrogenabstraction reactivity, i.e., the ability to abstract hydrogensintermolecularly. The beneficial effect is important when macromersystems containing these initiators are used as tissue adhesives,endovascular paving, formation of barriers to prevent post-surgicaladhesions, or any application involving the “adhesion” of the matrix toone or more surfaces. Since initiators exhibiting this type ofreactivity can abstract hydrogens from adjacent molecules, when amacromer system containing polymeric initiators of this type is appliedto a substrate, photoactivation of the system causes the abstraction ofhydrogens from the substrate by the initiators, thus forming a freeradical on the substrate and a free radical on the initiator. Thisdiradical can subsequently collapse forming a covalent bond between themacromer system and the substrate.

[0063] Other initiator groups on the same macromer initiate free radicalreactions with other macromers resulting in the formation of acrosslinked matrix covalently bound to the surface. Initiator groupsexhibiting this type of reactivity include analogs of benzophenone andthioxanthone. As can be readily understood, only polymeric initiatorsare capable of accomplishing this adhesion of the matrix to a surface,low molecular weight analogs of these initiators cannot produce thisphenomenon.

[0064] Optionally, the use of initiators for initiating the necessaryradical chain polymerization, can include the addition of one or moremonomeric polymerization accelerants to the polymerization mixture, theaccelerants serving to enhance the efficiency of polymerization.Polymerization accelerants useful in the present invention are typicallymonomers, which improve the reactivity of the macromer systems.Polymerization accelerants that have found particular utility for thisapplication are N-vinyl compounds, particularly N-vinyl pyrrolidone andN-vinyl caprolactam. Such accelerants can be used, for instance, at aconcentration of between about 0.01% and about 5%, and preferablybetween about 0.05% and about 0.5%, by weight, based on the volume ofthe macromer system.

[0065] In another embodiment, the polymeric initiator comprises apolymeric backbone with pendent initiator groups and pendent reactive oraffinity groups. These reactive or affinity groups enable the polymericinitiator to bind to target groups on surfaces of interest. This allowsthe polymeric initiator to bind to the surface of interest. In thismanner, interfacial polymerization of macromers can be accomplished. Asolution of polymeric initiator-containing pendent reactive or affinitygroups is applied to a surface with target sites. The reactive oraffinity groups on the polymeric initiator react with the sites on thesurface causing the polymeric initiator to bind to the surface. Excesspolymeric initiator can then be washed away. A solution of apolymerizable macromer is then applied to the surface. When light energyin applied to the system, a free radical polymerization reaction isinitiated only at the surface of interest. By varying the concentrationof the polymerizable macromer and the illumination time, the thicknessand crosslink density of the resulting matrix on the surface can bemanipulated.

[0066] Generally, there are two methods by which an initiator group canbe incorporated into a polymeric backbone. The first method involves theformation of a monomer which includes the initiator. This can beaccomplished readily using standard chemical reactions. For example, theacid chloride analog of an initiator can be reacted with anamine-containing monomer, to form a monomer which contains theinitiator.

[0067] The second method of incorporating initiator groups into apolymeric backbone involves coupling a reactive analog of the initiatorwith a preformed polymer. For example, an acid chloride analog of aninitiator can be reacted with a polymer containing pendent amine groupsforming a polymer bearing pendent initiator groups.

[0068] Macromer systems can be applied to a tissue site and/or implantarticle in any suitable manner, including by spraying, dipping,injecting or brushing the macromer system. Polymeric matrices preparedfrom macromer systems can be used in a variety of applications,including:

[0069] Cellular Encapsulation.

[0070] The use of hydrogels to form micro- or macrocapsules containingcells and other tissue, is well documented in the literature.Applications include the treatment of diabetes, Parkinson's disease,Alzheimer's disease, ALS, chronic pain, and others. Descriptions ofcellular encapsulation methods can be found throughout the patent andscientific literature. The use of the instant invention provides methodsof encapsulating cells in two basic ways.

[0071] 1) Bulk Polymerization

[0072] In this embodiment, cellular material is mixed in a solution ofthe macromer system and energy subsequently added to activate initiationof free radical polymerization. Prior to initiation, the solutioncontaining the macromer system with suspended cellular material, can beplaced in molds, shaped in particular geometric shapes, or placed insidea preformed membrane system, such as a hollow fiber. Upon illuminationor other energy addition, the initiation of free radical polymerizationcauses the macromer system to gel, forming a cell-containing matrix inthe desired shape. When formed into free-standing geometric shapes, theformulation of the macromer system can be designed to provide thedesired degrees of durability and permselectivity to the subsequentlyformed matrix. When formed inside membrane structures, such as hollowfibers designed to provide the desired permselectivity, the macromersystem can be formulated to provide the desired characteristics of thecell-suspending matrix, such as biocompatibility, etc.

[0073] 2) Interfacial Polymerization

[0074] In this embodiment, a membrane is formed directly on the surfaceof the cellular material. A solution of polymerizable ornon-polymerizable polymeric initiator-containing pendent affinity groups(e.g., positively charged groups) is mixed with the cellular material.The affinity groups bind to the sites on the surface of the cellularmaterial. The excess polymeric initiator is subsequently washed away andthe cellular material suspended in a solution of polymerizable macromer.Since initiator groups are present only at the surface of the cellularmaterial, when light energy is applied, polymerization is initiated onlyat the surface:macromer interface. By manipulating the duration ofillumination and macromer formulation, a polymeric matrix exhibiting thedesired characteristics of thickness, durability, permselectivity, etc.is formed directly on the surface of the cellular material.

[0075] Adhesives and Sealants.

[0076] Polymeric matrix systems have also found extensive use asadhesives for tissue and other surfaces. For this application, asolution of a macromer system is applied to a surface to which adhesionis desired, another surface is contacted with this surface, andillumination is applied forming a surface-to-surface junction. If atemporary adhesive is desired, the macromer system can be composed ofdegradable macromers.

[0077] Barriers.

[0078] Polymeric matrices can be used for the formation of barriers onsurfaces for various applications. One such application is a barrier forthe prevention of tissue adhesions following surgery. For thisapplication, a macromer system in liquid form is applied to the surfaceof damaged tissue. The liquid is illuminated to polymerize themacromers. The polymeric matrix prevents other tissue from adhering tothe damaged tissue. Both degradable and non-degradable macromer systemscan be used for this purpose. As described above, both bulkpolymerization and interfacial polymerization methods can be used toprepare surface coatings of this type.

[0079] Controlled Release Carriers.

[0080] Polymeric matrices find wide application as controlled releasevehicles. For this application, a solution of a macromer system anddrug, protein, or other active substance is applied to a surface. Thesolution is illuminated to polymerize the macromers. The polymericmatrix contains the drug, when exposed to a physiological or otherliquid-containing environment, the drug is slowly released into theenvironment. The release profile of the entrained drug can bemanipulated by varying the formulation of the macromer system. Bothdegradable and non-degradable macromer systems can be utilized for thispurpose. Likewise, both bulk and interfacial polymerization techniquescan be used to prepare controlled drug-releasing surfaces. In analternative embodiment, a drug or other active substance can be imbibedby a preformed matrix on a surface. The absorption and releasecharacteristics of the matrix can be manipulated by varying thecrosslink density, the hydrophobicity of the matrix, and the solventused for imbibition.

[0081] Alternatively, drug-containing polymeric microspheres can beprepared using standard techniques. A wide range of drugs and bioactivematerials can be delivered using the invention which include but are notlimited to, antithrombogenic, anti-inflammatory, antimicrobial,antiproliferative, and anticancer agents, as well as growth factors,morphogenic proteins, and the like.

[0082] Tissue Replacement/Scaffolding.

[0083] Polymeric matrices have found utility as three-dimensionalscaffolding for hybrid tissues and organs. For this application, amacromer system in liquid form is applied to a tissue defect andsubsequently illuminated to polymerize the macromers forming a matrixupon which ingrowing cells can migrate and organize into a functionaltissue. In one embodiment, the macromer system additionally includes agrowth factor which is slowly released and stimulates the ingrowth ofdesired cell types. In another embodiment, the macromers include pendentextracellular matrix peptides which can stimulate the ingrowth ofdesired cell types. A third embodiment would include both of the abovefeatures. An alternative embodiment includes cells included in thematrix with or without additional growth factor. The scaffolding can begenerated in vitro by placing the liquid macromer system in a mold orcavities in a device, or can be generated in vivo by applying the liquidmacromer system to a tissue defect. Both degradable and non-degradablemacromer systems could be used for this application, but degradablematrices are preferred.

[0084] Wound Dressing.

[0085] Polymeric matrices have been used extensively as superior wounddressing preparations. Currently, hydrogel and hydrocolloid wounddressing materials are being increasingly used due to their superiorwound healing properties. For this application, a macromer system inliquid form is applied to the wound site and subsequently formed into aflexible polymeric matrix upon exposure to light. When applied as aliquid, the macromer preparation conforms to the irregular surface ofthe wound. Upon illumination, a flexible matrix is formed which iscompletely conformal to the surface of the wound; no fluid-filledpockets which can act as sites of bacterial infiltration can exist. Inone embodiment, the macromer system additionally includes one or moretherapeutic agents, such as growth factors or antimicrobial agents whichare slowly released into the wound. Both degradable and non-degradablemacromer systems can be used for this application.

[0086] In Situ Device Formation.

[0087] Polymeric materials can be implanted into the body to replace orsupport the function of diseased or damaged tissues. One example of thisis the use of hollow cylindrical polymeric devices to support thestructure of a coronary artery following percutaneous transluminalcoronary angioplasty (PTCA). Currently, preformed cylindrical devicesare implanted via catheter insertion followed by balloon expansion tosecure the device. The expanded device supports the structure of theartery and prevents the reversion of the artery to the closed position(restenosis).

[0088] For this application, a liquid macromer preparation could beapplied to an injured artery via a multi-lumen catheter containing anillumination element. After application of the liquid macromer system tothe injured tissue, a semi-rigid polymeric matrix can be formed by abrief illumination. Upon removal of the catheter, a hollow, cylindrical,conformal polymeric device remains to support the artery and preventrestenosis. In one embodiment, the macromer system additionally includesa releasable therapeutic agent or agents, such as antiproliferativeand/or antithrombotic drugs. These agents are slowly released from theformed matrix, to provide additional therapeutic benefit to the injuredtissues. Both degradable and non-degradable macromer systems can be usedfor this application.

[0089] The invention will be further described with reference to thefollowing non-limiting Examples. It will be apparent to those skilled inthe art that many changes can be made in the embodiments describedwithout departing from the scope of the present invention. Thus thescope of the present invention should not be limited to the embodimentsdescribed in this application, but only by embodiments described by thelanguage of the claims and the equivalents of those embodiments. Unlessotherwise indicated, all percentages are by weight

EXAMPLES Example 1 Synthesis of 7-Methyl-9-oxothioxanthene-3-carboxylicAcid Chloride (MTA-Cl)

[0090] The 7-methyl-9-oxothioxanthene-3-carboxylic acid (MTA), 50.0 g(0.185 mol), was dissolved in 350 ml of toluene and 415 ml (5.69 mol) ofthionyl chloride using an overhead stirrer in a 2 liter 3-neck roundbottom flask. N,N-Dimethylformamide (DMF), 2 ml, was added and thereaction was brought to reflux for 2 hours. After this time, the mixturewas stirred at room temperature for 16 hours. The solvent was removedunder vacuum and the product was azeotroped with 3×350 ml of toluene toremove the excess thionyl chloride. The product was recrystallized from800 ml of chloroform and the resulting solid was placed in a vacuum ovenfor 16 hours at 45° C. to complete removal of solvent. The isolatedproduct weighed 45.31 g (85% yield) and nuclear magnetic resonancespectroscopy (NMR) confirmed the desired structure. This product wasused for the preparation of a photoreactive monomer as described inExample 2.

Example 2 Synthesis ofN-[3-(7-Methyl-9-oxothioxanthene-3-carboxamido)propyl]methacrylamide(MTA-APMA)

[0091] The N-(3-aminopropyl)methacrylamide hydrochloride (APMA), 4.53 g(25.4 mmol), was suspended in 100 ml of anhydrous chloroform in a 250 mlround bottom flask equipped with a drying tube. After cooling the slurryin an ice bath, the MTA-Cl, 7.69 g (26.6 mmol), was added as a solidwith stirring. A solution of 7.42 ml (53.2 mmol) of triethylamine (TEA)in 20 ml of chloroform was then added over a 1.5 hour time period,followed by a slow warming to room temperature. The mixture was allowedto stir 16 hours at room temperature under a drying tube. After thistime, the reaction was washed with 0.1 N HCl and the solvent was removedunder vacuum after adding a small amount of phenothiazine as aninhibitor. The resulting product was recrystallized from tetrahydrofuran(THF)/toluene (3/1) and gave 8.87 g (88.7% yield) of product after airdrying. The structure of the compound was confirmed by NMR analysis.

Example 3 Preparation of N-Succinimidyl 6-Maleimidohexanoate(MAL-EAC-NOS)

[0092] 6-Aminohexanoic acid, 100.0 g (0.762 moles), was dissolved in 300ml of acetic acid in a three-neck, 3 liter flask equipped with anoverhead stirrer and drying tube. Maleic anhydride, 78.5 g (0.801moles), was dissolved in 200 ml of acetic acid and added to the6-aminohexanoic acid solution. The mixture was stirred one hour whileheating on a boiling water bath, resulting in the formation of a whitesolid. After cooling overnight at room temperature, the solid wascollected by filtration and rinsed with 2×50 ml of hexane. After drying,the typical yield of the (Z)-4-oxo-5-aza-2-undecendioic acid was 158-165g (90-95%) with a melting point of 160-165° C. Analysis on an NMRspectrometer was consistent with the desired product.

[0093] (Z)-4-Oxo-5-aza-2-undecendioic acid, 150.0 g (0.654 moles),acetic anhydride, 68 ml (73.5 g, 0.721 moles), and phenothiazine, 500mg, were added to a 2 liter three-neck round bottom flask equipped withan overhead stirrer. Triethylamine, 91 ml (0.653 moles), and 600 ml ofTHF were added and the mixture was heated to reflux while stirring.After a total of 4 hours of reflux, the dark mixture was cooled to <60°C. and poured into a solution of 250 ml of 12 N HCl in 3 liters ofwater. The mixture was stirred 3 hours at room temperature and then wasfiltered through a Celite 545 pad to remove solids. The filtrate wasextracted with 4×500 ml of chloroform and the combined extracts weredried over sodium sulfate. After adding 15 mg of phenothiazine toprevent polymerization, the solvent was removed under reduced pressure.The 6-maleimidohexanoic acid was recrystallized from hexane/chloroform(2/1) to give typical yields of 76-83 g (55-60%) with a melting point of81-85° C. Analysis on a NMR spectrometer was consistent with the desiredproduct.

[0094] The 6-maleimidohexanoic acid, 20.0 g (94.7 mmol), was dissolvedin 100 ml of chloroform under an argon atmosphere, followed by theaddition of 41 ml (0.47 mol) of oxalyl chloride. After stirring for 2hours at room temperature, the solvent was removed under reducedpressure with 4×25 ml of additional chloroform used to remove the lastof the excess oxalyl chloride. The acid chloride was dissolved in 100 mlof chloroform, followed by the addition of 12.0 g (0.104 mol) ofN-hydroxysuccinimide and 16.0 ml (0.114 mol) of triethylamine. Afterstirring overnight at room temperature, the product was washed with4×100 ml of water and dried over sodium sulfate. Removal of solvent gave24.0 g (82%) of MAL-EAC-NOS which was used without further purification.Analysis on an NMR spectrometer was consistent with the desired product.

Example 4 Preparation of a Copolymer of MTA-APMA, MAL-EAC-NOS, andN-Vinylpyrrolidone

[0095] A polymeric initiator is prepared by copolymerization of amonomer charge consisting of 5 mole % MTA-APMA, 10 mole % MAL-EAC-NOS,and 85 mole % N-vinylpyrrolidone (VP). The polymerization is run informamide or other suitable solvent using 2,2′-azobisisobutyronitrile(AIBN) as an initiator and N,N,N′,N′-tetramethylethylenediamine (TEMED)as an oxygen scavenger. Mercaptoethanol is added as a chain transferreagent at a concentration designed to give a molecular weight between2,000 and 20,000 daltons. Upon completion of the polymerization, thecopolymer is precipitated by addition of ether or other non-solvent forthe polymer. After isolation by filtration, the product is washedextensively with the precipitating solvent to remove residual monomersand low molecular weight oligomers. The copolymer is dried under vacuumand is stored desiccated to protect the hydrolyzable N-oxysuccinimide(NOS) esters.

Example 5 Synthesis of a Photoreactive Macromer Derived from aPoly(caprolactone-co-lactide) Derivative of Pentaerythritol Ethoxylate

[0096] A 15 gram scale reaction was performed by charging a thick-walledtube with 8.147 g (56.5 mmol) of 1-lactide(3,6-dimethyl-1,4-dioxane-2,5-dione) and 6.450 g (56.5 mmol) ofε-caprolactone. To this mixture was added 0.402 g (1.49 mmol) ofpentaerythritol ethoxylate (ave. MW appprox. 270) to providepolymerization sites and control molecular weight. This mixture waswarmed gently until dissolution of all reagents was complete. Thecatalyst, stannous 2-ethylhexanoate (0.015 ml) was added and thereaction vessel sealed. The reaction mixture was warmed to 150° C. andstirred for 20 hours. The resulting polymer was dissolved in chloroformand dialyzed against methanol using 1000 MWCO dialysis tubing. Afterdialysis, the solvent was removed in vacuo. The purified polymer wasdissolved in chloroform and treated with 2.41 g (23.8 mmol) of TEA. Tothis reaction mixture was added 292 mg (1.19 mmol) of 4-benzoylbenzoylchloride (BBA-Cl) and the resulting mixture was stirred for 16 hours. Tothis reaction mixture was added 0.734 g (8.11 mmol) of acryloyl chlorideand the reaction was stirred an additional 8 hours. The modified polymerwas purified by dialysis against methanol using 1000 MWCO dialysistubing. After dialysis, the solvent was removed in vacuo and the polymer(15.36 grams) stored desiccated at room temperature.

Example 6 Synthesis of Water Soluble Siloxane Macromer with PendentInitiator Groups

[0097] Fifty grams of a water-soluble siloxane macromer with pendentinitiator groups were synthesized by first dissolving 50 grams ofcommercially available poly[dimethylsiloxane-co-methyl(3-hydroxypropyl)siloxane]-graft-poly(ethylene glycol) 3-aminopropylether (Aldrich Chemical) in 50 ml of methylene chloride. To thissolution was added 5.0 g (49 mmol) of TEA. The reaction solution wascooled to −50° C., then transferred to a stir plate at room temperature.MTA-Cl, 1.0 g (3.5 mmol), prepared according to the general method inExample 1, and 5.0 g (55 mmol) of acryloyl chloride were added and thesolution was stirred for 6 hours at room temperature. The solution wasdialyzed against deionized water using 3500 MWCO dialysis tubing and thewater was subsequently removed in vacuo. The product (48.4 grams) wasstored desiccated at room temperature.

Example 7 Synthesis of a Polymerizable Hyaluronic Acid

[0098] Two grams of hyaluronic acid (Lifecore Biomedical, Chaska, Minn.)were dissolved in 100 ml of dry formamide. To this solution were added1.0 g (9.9 mmol) of TEA and 4.0 g (31 mmol) of glycidyl acrylate. Thereaction mixture was stirred at 37° C. for 72 hours. After exhaustivedialysis against deionized water using 12-14k MWCO dialysis tubing, theproduct (2.89 grams) was isolated by lyophilization.

Example 8 Preparation of a Photoderivatized Polyacrylamide (Photo-PAA)

[0099] Acrylamide, 10.24 g (0.144 mol), was dissolved in 200 ml ofdeionized water. To the solution was added 0.279 g (1.56 mmol) of APMA,0.33 g (1.45 mmol) of ammonium persulfate and 0.155 g (1.33 mmol) ofTEMED. The solution was evacuated in a filter flask with a wateraspirator for 10 minutes. The tubing was clamped and the solution leftunder vacuum for one hour. The resulting polymer solution was dialyzedagainst deionized water using 12-14k MWCO dialysis tubing. To 150 ml ofpolymer solution in a PTFE bottle containing 3.0 grams of polymer wasadded 0.504 ml (3.62 mmol) of TEA. To this solution was added 30 ml of28.4 mg/ml (3.48 mmol) 4-benzoylbenzoyl chloride in CHCl₃. The bottlewas capped tightly and shaken for one hour. The bottle was thencentrifuged for 10 minutes to separate the phases after which theaqueous layer was removed, dialyzed against deinoized water using 12-14kMWCO dialysis tubing, and lyophilized. The product (3.21 grams) wasstored, dessicated at room temperature.

Example 9 Synthesis of the N-Hydroxysuccinimide Ester of Eosin Y

[0100] Eosin Y, 1.00 g (1.54 mmol), was dissolved in 10 ml dry dioxanewith stirring, gentle warming and some sonication. After the solutionwas complete, the orange solution was cooled to room temperature underargon. N-Hydroxysuccinimide, 0.195 g (1.69 mmol), and1,3-dicyclohexylcarbodiimide, 0.635 g (3.08 mmol), were added as solids.The resulting red mixture was stirred at room temperature for 48 hoursunder an inert atmosphere. After this time the solid was removed byfiltration and washed with dioxane. The filtrate was concentrated invacuo to give 1.08 g (94% yield) of a glassy red solid.

Example 10 Synthesis of a Copolymer of APMA, Methyl Methacrylate, andN-Vinylpyrrolidone Followed by Addition of Acryloyl Groups

[0101] The following ingredients for the copolymer were placed in aglass vessel and dissolved in 20 ml DMSO: APMA (2.68 g, 15.0 mmol), VP(6.74 ml, 63.1 mmol), methyl methacrylate (mMA) (0.334 ml, 3.12 mmol),mercaptoethanol (0.053 ml, 0.76 mmol), AIBN (0.041 g, 0.25 mmol), andTEMED (0.057 ml, 0.38 mmol). After solution was complete, the monomersolution was degassed, blanketed with argon and placed in an agitatingincubator at 55° C. The copolymer was dialyzed against deionized waterin 6-8,000 MWCO dialysis tubing. The W dialyzed solution (˜400 ml) wasloaded with acrylate groups. TEA, 5.0 ml (35.9 mmol), was added withstirring. The solution was placed in a freezer for 5-10 minutes to cool.After this time, 5.0 ml (61.5 mmol) of acryloyl chloride in 5 ml ofchloroform were added with stirring. The reaction mixture was stirred atroom temperature for 16 hrs. After this time the acrylated polymer wasdialyzed against deionized water using 6-8,000 MWCO tubing. The productwas lyophilized and 7.10 g were obtained.

Example 11 Synthesis of a Copolymer of MTA-APMA, APMA, MethylMethacrylate, and N-Vinylpyrrolidone Followed by Addition of AcryloylGroups

[0102] The following ingredients for the copolymer were placed in aglass vessel and dissolved in 20 ml DMSO: MTA-APMA (0.613 g, 1.55 mmol),APMA (2.578 g, 14.4 mmol), VP (6.27 ml, 58.7 mmol), mMA (0.319 ml, 2.98mmol), mercaptoethanol (0.054 ml, 0.77 mmol), AIBN (0.039 g, 0.24 mmol),and TEMED (0.053 ml, 0.35 mmol). After solution was complete, themonomer solution was degassed, blanketed with argon and placed in anagitating incubator at 55° C. The copolymer was dialyzed againstdeionized water in 6-8,000 MWCO dialysis tubing. The dialyzed solutionwas protected from light and loaded with acrylate groups. TEA, 5.0 ml(35.9 mmol), was added with stirring. The solution was placed in afreezer for 5-10 minutes to cool. After this time, 5.0 ml (61.5 mmol) ofacryloyl chloride in 5 ml of chloroform were added with stirring. Thereaction mixture was stirred at room temperature for 9 hrs. After thistime the acrylated polymer was dialyzed against deionized water using6-8,000 MWCO tubing and protected from light. The product (8.88 grams)was isolated by lyophilization.

Example 12 Evaluation of Matrix Formation

[0103] A 15% solution of the co-polymer from Example 11 was prepared in10% DMSO/water. The MTA content of the solution was estimated bymeasuring the absorbance of the solution at 395 nm(A@395 nm=42.6).A 15%solution of the co-polymer from Example 10 (same co-polymer as thatdescribed in Example 11 but with no MTA-APMA) was prepared in 10%DMSO/water. MTA was added to this solution until its absorbance at 395nm matched that of the solution described above. The two solutions wereidentical in concentration of co-polymer and photoinitiator, the onlydifference between them being that in one solution the photoinitiatorwas present in polymeric form(POLY) and in the other the photoinitiatorwas present in non-polymeric form(NON).

[0104] In order to compare the matrix forming ability of the twosolutions the following evaluation was undertaken: the indentations inthe lid of a 96 well microtiter plate were used as miniature molds toevaluate the ability of the photoreactive polymer solutions to formsolid hydrogel discs upon illumination. The indentations are eightmillimeters in diameter and approximately 0.6 millimeters deep. 30microliters of polymer solution will just fill the indentatation. Thirtymicroliters of both the (POLY) and (NON) solutions were added to wells.After addition of the polymer solutions, the lids were illuminated usingan EFOS Ultracure 100 SS illumination system equipped with a 400-500 nmfilter, for varying lengths of time. After illumination the lid wasflooded with water and each polymer formulation rated for its ability toform solid discs using the following arbitrary scale:

[0105] 0=liquid, no gelation

[0106] 1=soft gel, unable to remove from mold

[0107] 2=firm gel, removable from mold with slight difficulty

[0108] 3=very firm gel, easily removed from mold

[0109] 4=very firm gel, elastomeric properties evident

[0110] Results: Matrix formation Time(sec) Polymer 2 5 10 30 60 120(POLY) 1 2 3 4 4 4 (NON) 0 0 1 2 3 3

[0111] The polymer solution containing the polymer-bound initiator(POLY)formed matrices more rapidly and more completely than the polymersolution containing non-polymer-bound initiator(NON) when exposed tolight energy.

Example 13 Synthesis of an Eosin Substituted Polymer

[0112] N-Vinylpyrrolidone, 10.0 g (90.0 mmol), was dissolved in 50 mlDMSO. To the solution was added 0.30 g (1.68 mmol) of APMA, 0.15 g (0.91mmol) of AIBN, and 0.10 g (0.86 mmol) of TEMED. The solution was spargedwith nitrogen for 20 minutes and incubated at 55° C. for 20 hours. Theresulting polymer was purified by dialysis against water and isolated bylyophiliaztion.

[0113] Three grams of the polymer were dissolved in 150 mls dry dioxane.To this solution was added 0.504 ml (3.62 mmoles) of TEA. Subsequently,2.74 grams (3.5 mmoles) of the N-hydroxysuccinimide ester of Eosin Y wasadded and the reaction mixture stirred for two hours at roomtemperature. The solution was dialyzed against dH20 using 12-1 4kdacut-off dialysis tubing and lyophilized to isolate the product. Thereaction yielded 3.96 grams of red polymer.

Example 14 A Biodegradable Tissue Adhesive

[0114] A solution was prepared consisting of 5% polymerizable hyaluronicacid (Example 7) and 2% photoderivatized polyacrylamide (Example 8) inwater. This reagent was evaluated for use as a tissue adhesive usingcellulose dialysis tubing as a tissue model.

[0115] Shear strength testing was performed on dialysis tubing. Thetubing was slit and cut into 2 cm×4 cm pieces. The pieces were soaked inwater briefly, removed, and tested while still damp. One piece was laidflat on a surface and 10 μl of adhesive applied to one end of the strip.Another piece was laid over this piece with a 1 cm overlap betweenpieces. When evaluating the photoactivatable adhesive (2/5 HA), theoverlap area was illuminated for 10 seconds. When evaluating a controladhesive, the adhesive was allowed to set for five minutes. The bondedsamples were mounted in a tensiometer lengthwise by the ends such thatthe plane of the area of adhesive was parallel to the axis of thetensiometer. The samples were extended at the rate of 1 cm/minute untiladhesive or substrate failure, and the force at failure recorded.Substrate-only, and, for photoactivatable adhesive, non-illuminatedsamples, were included as controls in the evaluations. Maximum ForceAdhesive Failed Substrate Failed Adhesive Generated Kg Before SubstrateBefore Adhesive 2/5 HA 0.53 0/4 4/4 2/5 HA (no 0.081 4/4 0/4illumination) Fibrin glue 0.045 4/4 0/4 Cyanoacrylate 0.49 0/4 4/4

Example 15 Formation of an in Situ Hydrogel Wound Dressing

[0116] Photopolymerizable, matrix-forming reagents were evaluated forefficacy as in situ wound dressings.

[0117] Preparation of reagents:

[0118] An experimental in situ forming wound dressing was prepared by:

[0119] 1) Dissolving reactive macromer from Example 10 at 20% into asterile 6% glycerin solution in water.

[0120] 2) Preparing a sterile solution of polymeric eosin reagent fromExample 12 at 4% in water and a sterile solution of 2M triethanolamine(TEA) in water.

[0121] 3) Transporting the three sterile solutions to a surgical suitefor application to wound sites created on porcine skin.

[0122] Four young female China White swine weighing between 15-20 kgwere anesthetized and 12 wounds inflicted on one side of each pig.Wounds were 1″×2″ and 0.015″ deep and were inflicted by a calibratedelectrodermatome (Padgett). The wounds were inflicted in two rows of sixon the thoracic and paravertebral area of each pig, leavingapproximately two inches between adjacent wounds. The wounds wererandomized and received one of three treatments:

[0123] 1) No treatment (control)

[0124] 2) Application of OpSite®, a semi-occlusive wound dressing fromSmith and Nephew, Inc.

[0125] 3) Experimental photo-curable dressing

[0126] To apply the experimental dressing, 0.5 mls of thepolymeric-eosin solution and 0.5 mls of the TEA solution were added tothe macromer/glycerin solution yielding a photo-wound dressing solution.The solution was transferred to 16 three ml sterile syringes (2ml/syringe) and one syringe was used to application to each wound site.The solutions were applied to each assigned wound site (approximately1.5 mls solutions/site) and allowed to flow over the site. The solutionswere fixed by illumination with a 150 W incandescent light bulbpositioned four inches from the wound surface for 30 seconds. Thedressing solution readily formed into a durable, rubbery hydrogel whichadhered very well to the wound sites. Sterile 4×4 gauze pads were placedover the entire wounded area of each pig, and the pigs placed in sterilestockinettes. On selected days (3, 4, 5, and 7), one pig was euthanizedand the effect of dressing on wound epithelialization and repairevaluated.

[0127] Evaluation of effect of dressing on wound epithelialization andrepair:

[0128] Following euthanasia, skin wounds were removed from theunderlying deep subcutaneous tissue and fixed in 10% neutral bufferedformalin solution. After fixation, five biopsy sites from each woundwere obtained with a 6 mm Keys skin biopsy punch. Each biopsy waspackaged, labeled and submitted for histological sectioning.Histological sections were sectioned at 4 microns and stained withhematoxylin and eosin. Histological sections were examined with themicroscope without knowing the type of covering placed over the woundsite. The following criteria were evaluated and scored in microscopicexamination:

[0129] Degree of epithelialization of the wound

[0130] Magnitude of the inflammatory reaction

[0131] Degree of fibroplasia in the wound

[0132] Degree of damage to subcutaneous tissue:

[0133] Morphometric analysis of cell types in the histological sectionswere used to help differentiate the degree of inflammatory reactionpresent. The number of polymorphonuclear cells, lymphocytic cells, andfibroblasts was evaluated. Each histological biopsy was graded on ascale of 1-5.

[0134] Degree of inflammatory reaction:

[0135] 1. No or borderline cellular inflammatory reaction

[0136] 2. Minimal inflammation

[0137] 3. Moderate density of inflammatory cells with some exudate

[0138] 4. Severe, high density of inflammatory cells in or on the woundtissue with thicker layer of exudate

[0139] 5. Excessive inflammation, with signs of dense foci ofinflammatory cells infiltrating the wound tissue or on the wound andforming a thick layer of inflammatory exudate.

[0140] Degree of wound epithelialization:

[0141] 1. Stratum comeum present at least 4 layers of cells and entireepidermal surface is present.

[0142] 2. Stratum comeum is present at least 1 layer of cells and entireepidermal surface is present.

[0143] 3. Stratum comeum is present at least 1 layer of cells and ½ ofepidermal surface is covered.

[0144] 4. No stratum comeum is present; minimal inflammation of thesubepidermal tissue.

[0145] 5. No stratum comeum is present; moderate inflammation insubepidermal tissue.

[0146] Degree of fibroplasia in the wound:

[0147] 1. No fibroplasia in the wound

[0148] 2. Mild fibroplasia in the wound involving ⅓ to ½ wound surface

[0149] 3. Mild fibroplasia in the wound involving ⅔ or more of the wound

[0150] 4. Moderate fibroplasia involving ⅓ to ½ of the wound

[0151] 5. Severe fibroplasia involving ½ or more of the wound

[0152] Degree of damage to the subcutaneous tissue:

[0153] 1. No damage to the subcutaneous tissue

[0154] 2. Mild damage to the subcutaneous tissue with mild edema and fewinflammatory cells.

[0155] 3. Moderate damage to the subcutaneous tissue with moderate edemaand moderate accumulation of inflammatory cells

[0156] 4. Severe damage to the subcutaneous tissue with severe edema andlarge number of inflammatory cells

[0157] 5. Excessive damage to the subcutaneous tissue with dense foci ofinflammatory cells

[0158] Results:

[0159] Each biopsy was graded blindly using the criteria listed above.When the histological examination was completed, the graded biopsieswere correlated with the wound sites. A single average score for eachdressing was calculated by adding all the scores for every site for eachdressing and dividing by the number or scores.

[0160] The total scores for each type of wound dressing on days 3, 4, 5,and 7 were evaluated with an ANOVA SAS program for data intervals tostatistically evaluate if there was any difference between the threetypes of wound treatments administered. Only two scores were found to bestatistically significant:

[0161] 1. On day 4 following wound creation the mean for the OpSite@dressing was 2.4 and was found to be statistically significant whencompared to the control and experimental wound sites.

[0162] 2. On day 7 following the creation of the wounds the mean for theexperimental dressing, 1.8 was found to be statistically significantwhen compared to the control and the OpSite® wound dressings.

[0163] On day 7 post-wound creation, the wound sites treated with theexperimental photocurable dressing showed significantly superior healingto those that were untreated or treated with OpSite® dressing, as judgedby the criteria described.

Example 16 A Bioresorbable Drug Delivery Coating.

[0164] A solution of 33% of the macromer from Example 5 was prepared inethanol. Ten centimeter lengths of polyurethane rod (PU) were dippedinto the macromer solutions and illuminated for six minutes to form amatrix. This procedure resulted in the formation of a very durable,tenacious, and flexible coating on the rod. One gram of chlorhexidinediacetate (an antimicrobial agent) was dissolved in 10 mls of themacromer solution and the coating process repeated on additional PUrods. This also resulted in a tenacious, durable, and flexible coatingon the rods. The rods were cut into one centimeter pieces and evaluatedin a zone of inhibition analysis.

[0165] Coated dye-containing pieces, coated no-drug controls, anduncoated pieces were placed in Mueller-Hinton agar plates which wereswabbed with a 10⁶ suspension of Staphylococcus epidermidis (ChristensenRP62A). These pieces functioned as unwashed controls and weretransferred to freshly swabbed agar plates each day for 60 days.

[0166] Additional pieces, no-drug controls (both coated and uncoated)and drug-incorporated coated, wer placed in snap-cap vials and washedwith 50% Normal Calf Serum in PBS. The tubes were placed on an orbitalshaker and incubated at 37° C. and 200 rpm for 20 days. Each day thewash solution was removed and replaced with fresh solution.Periodically, pieces were removed from the serum/PBS and placed in agaras described above. Zones of inhibition resulting from these pieces wererecorded and compared to the zones produced by unwashed pieces.

[0167] The no-drug coated control pieces, both coated and uncoated,produced no zones. On day 0, both washed and unwashed drug-incorporatedpieces produced zone of 24.5 mm. On day 20, when the final washed pieceswere evaluated, the unwashed pieces were producing zones of 17.5 mm, andthe washed pieces were producing zones of 9.5 mm. On day 60, when theexperiment was terminated, the unwashed pieces were still producingzones of 17 mm.

[0168] This experiment demonstrates the utility of this matrix-formingpolymer at producing drug delivery coatings which provide a long-termdelivery of a bioactive agent.

Example 17 A Biostable Drug Delivery Coating

[0169] A solution of 25% of the macromer from Example 6 was prepared in50% IPA/H₂O. Ten centimeter lengths of polyurethane rod were dipped intothe macromer solution and illuminated for six minutes to form matrix.This procedure resulted in the formation of a very durable, tenacious,and flexible coating on the rod. Five hundred milligrams ofchlorhexidine diacetate was dissolved in 10 mls ethanol. Half of thecoated rods were soaked in this solution for 60 minutes at roomtemperature, and half of the rods were soaked in neat ethanol under thesame conditions. After soaking, the rods were removed from the ethanoland allowed to dry for 20 hours at room temperature. The rods were cutinto one centimeter pieces and evaluated in a zone of inhibitionanalysis.

[0170] Uncoated control, coated control, and coated drug-incorporatedpieces were placed in Mueller-Hinton agar plates which were swabbed witha 10⁶ suspension of Staphylococcus epidermidis (Christensen RP62A).These plates were incubated for 20 hours at 37° C. The zone where nobacterial growth was evident around each piece was measured and thepiece transferred to a freshly swabbed agar plate each day for 14 days.

[0171] The uncoated control pieces and the coated control piecesproduced no zones. On day 0, the drug-incorporated coated piecesproduced average zones of 25 mm. These pieces continued to produce zoneseach day. On day 14, when the experiment was terminated, the piecesproduced average zones of 6 mm.

Example 18 Formation of a Three-Dimensional Device

[0172] One end of a 3 mm diameter teflon-coated rod was dipped to alevel of 1.5 cm in neatBBA-acryloylpolytetra(caprolactone-co-lactide)pentaerythritol ethoxylate(see Example 5) and immediately illuminated, with rotation, for 10seconds suspended between opposed Dymax lamps. After illumination, asemi-rigid elastomeric coating had formed on the rod. The rod was cooledto facilitate removal of the polymeric coating. The closed end of thecylinder was removed with a razor blade, thus forming a hollowcylindrical device of 1.25 cm in length and 3.5 mm in diameter.

Example 19 Synthesis of a Polymerizable Collagen

[0173] One gram of soluble collagen (Semed-S, Kensey-Nash Corp.) (amixture of Types I and III) was dissolved in 50 mls of 0.01 N HCl. Whendissolved, 1.25 gms triethylamine (12.4 mmoles) was added to thereaction mixture. One gram of acryloyl chloride (11.0 mmoles) dissolvedin one milliliter of methylene chloride was added to the reaction vesseland the mixture was stirred for 20 hours at room temperature.

[0174] The reaction mixture was dialyzed exhaustively against dH₂O, andthe product isolated by lyophilization. A yield of 1.17 grams ofpolymerizable collagen was realized.

Example 20 A Collagen Scaffolding that Contains a Bone MorphogenicProtein

[0175] A. Preparation of the Solidified Scaffolding.

[0176] A solution of liquid macromer is prepared which consists of 5%(w/v) of polymerizable collagen (Example 19) plus 1% (w/v) ofphotoderivatized polyacrylamide (prepared as described in Example 8) inphosphate buffered saline, pH 7.4. To this is added 50 μg/ml (0.005%w/v) of bone morphogenic protein (BMP-7 from a private source). Aliquotsof the above solution (150 μl) are then placed in molds (8 mm diameterand 3 mm high) and are illuminated for 10 seconds with a Dymax lamp (asdescribed in Example 13) to solidify the collagen scaffolding. Controldisks of solidified collagen scaffolding are prepared via the sameprotocol except that BMP-7 is not added.

[0177] B. Evaluation of the Solidified Scaffolding.

[0178] Disks of solidified collagen scaffolding with BMP-7 are evaluatedfor stimulation of bone growth in a rat cranial onlay implant model. Inthis model, the periosteal membrane is removed and the collagen disksare implanted on the cranium. After 30 days, the implants and adjacentcranial bone are removed, fixed in cold methanol, embedded in PMMA,sectioned, ground to 50-100 μm thickness, stained with Sandersons RapidBone Stain, and counterstained with Van Gieson's picro-fuchsin. Thisprotocol evaluates nondecalcified bone, with mature bone staining red,immature bone staining pink, cartilage staining blue-gray, andundegraded collagen appearing acellular and pale yellow.

[0179] One control consists of disks of solidified collagen scaffoldinglacking BMP-7. A second control consists of 150 μl of nonilluminatedliquid macromer solution which contains BMP-7 (the same solutioncomposition that was placed in molds and illuminated to produce thesolidified collagen scaffolding containing BMP-7).

[0180] When evaluated histologically at 30 days as described above, theexperimental disks (solidified collagen scaffolding containing BMP-7)show extensive bone formation in the space originally occupied by thecollagen disk. In contrast, both controls (the solidified collagenscaffolding lacking BMP-7 and the nonilluminated liquid control solutioncontaining BMP-7) show little or no bone formation. The amount of bonethat forms with the controls is less than 25% of that observed with theexperimental disks, therefore demonstrating that the solidified collagenscaffolding greatly enhances BMP-stimulated bone formation.

Example 21 Synthesis of a Polymerizable Collagen

[0181] Dissolved 0.5 gram collagen (insoluble bovine tendon collagen,Type I, ReGen Corp.) in 20 mls dry formamide by incubating for 20 hourson an orbital shaker at 37 degrees C. With stirring, added 1.0 gram (9.8mmol) TEA and equilibrated for 60 minutes in ice water bath. Withstirring, added 1.0 gram (11 mmol) acryloyl chloride, in 0.25 gramaliquots (1 aliquot/min). After the final addition, stirred in ice waterbath for 2 hours. Removed from ice water bath and continued to stir atroom temperature for 18 hours. The product was purified by dialysisagainst deionized water using 6-8K MWCO dialysis tubing, and isolated bylyophilization.

What is claimed is:
 1. A method of delivering an implant article to atissue site, the method comprising a) providing an article selected fromthe group consisting of tissue implants and prosthetic devices providinga porous surface, b) providing a crosslinkable macromer systemcomprising a polymerization initiator and one or more polymers havingpendent polymerizable groups, c) implanting the article within thetissue site with the macromer system positioned between the article andthe tissue, and d) polymerizing the macromer system to form acrosslinked matrix between the article and the tissue site suitable topermit continuous tissue growth through the matrix and between theimplant and the native tissue.
 2. A method according to claim 1 whereinthe macromer system is positioned upon the article prior to implantingthe article within the tissue site and is crosslinked before, during orafter implanting the article within the tissue site.
 3. A methodaccording to claim 1 wherein the macromer system is delivered to thetissue site and crosslinked before, during or after the implant articlehas been positioned within the tissue site.
 4. A method according toclaim 1 wherein a first amount of a macromer system is positioned uponthe article prior to implanting the article within the tissue site, anda second amount of either the same or different macromer system isdelivered to the tissue site, either before or after positioning theimplant article within the tissue site, and the first and second amountsare independently crosslinked before, during or after positioning theimplant within the tissue site.
 5. A method according to claim 1 whereinthe macromer system is applied to the tissue site and/or implant articleby spraying, dipping, injecting or brushing the macromer system.
 6. Amethod according to claim 1 wherein the polymer having pendentpolymerizable groups is prepared by a method that comprises the steps ofa) providing a polymer selected from the group consisting ofpolysaccharides and polyamino acids, and b) incorporating polymerizablegroups into the polymer by reaction of the polymer with a reactivemoiety containing an ethylenically unsaturated group capable ofundergoing free radical polymerization, wherein the reaction between thepolymer and reactive moiety is carried out in a medium comprising apolar organic solvent.
 7. A method according to claim 6 wherein thepolysaccharides are selected from the group consisting of hyaluronicacid, starch, dextran, heparin, chondroitin sulfate, dermatan sulfate,heparan sulfate, keratan sulfate, dextran sulfate, pentosan polysulfate,and chitosan, and the polyamino acids are selected from the groupconsisting of gelatin, collagen, fibronectin, laminin, albumin, elastin,and active peptide domains thereof.
 8. A method according to claim 7wherein the solvent comprises formamide.
 9. A method according to claim8 wherein the reactive moiety is selected from the group consisting ofglycidyl acrylate and acryloyl chloride.
 10. A method according to claim9 wherein the polymer comprises hyaluronic acid or collagen.
 11. Amethod according to claim 1 wherein the initiators comprisepolymer-pendent initiators.
 12. A method according to claim 1 whereinthe macromer system further comprises a polymerization acceleratorcomprising a N-vinyl compound.
 13. A method according to claim 1 whereinthe article is selected from joint implants, dental implants, softtissue cosmetic prostheses, wound dressings, vascular prostheses, andophthalmic prostheses.
 14. A method according to claim 13 wherein thearticle is a joint implant selected from the group consisting of hip andknee prosthetic devices having porous surfaces.
 15. A method accordingto claim 14 wherein the prosthetic device is fabricated from syntheticmaterials and the porous surface provides a three-dimensional structurehaving interconnected passages, with pores having an average pore sizeof between about 5 microns and about 1 mm in diameter.
 16. A methodaccording to claim 15 wherein the average pore size is between about 20microns and about 600 microns in diameter.
 17. A method of preparing apolymerizable macromer system comprising the steps of a) providing apolymer selected from the group consisting of polysaccharides andpolyamino acids, and b) incorporating polymerizable groups into thepolymer by reaction of the polymer with a reactive moiety containing anethylenically unsaturated group capable of undergoing free radicalpolymerization, wherein the reaction between the polymer and reactivemoiety is carried out in a medium comprising a polar organic solvent.18. A method according to claim 17 wherein the polysaccharides areselected from the group consisting of hyaluronic acid, starch, dextran,heparin, chondroitin sulfate, dermatan sulfate, heparan sulfate, keratansulfate, dextran sulfate, pentosan polysulfate, and chitosan, and thepolyamino acids are selected from the group consisting of gelatin,collagen, fibronectin, laminin, albumin, elastin, and active peptidedomains thereof.
 19. A method according to claim 18 wherein the solventcomprises formamide.
 20. A method according to claim 19 wherein thereactive moiety is selected from the group consisting of glycidylacrylate and acryloyl chloride.
 21. A method according to claim 20wherein the polymer comprises hyaluronic acid or collagen.
 22. A methodaccording to claim 17 wherein the initiators comprise polymer-pendentinitiators.
 23. A method according to claim 17 wherein the macromersystem further comprises a polymerization accelerator comprising aN-vinyl compound.
 24. A polymerizable macromer system comprising apolymer selected from the group consisting of polysaccharides andpolyamino acids wherein polymerizable groups have been incorporated intothe polymer by reaction of the polymer, in a medium comprising a polarorganic solvent, with a reactive moiety containing an ethylenicallyunsaturated group capable of undergoing free radical polymerization. 25.A macromer system according to claim 24 wherein the polysaccharides areselected from the group consisting of hyaluronic acid, starch, dextran,heparin, chondroitin sulfate, dermatan sulfate, heparan sulfate, keratansulfate, dextran sulfate, pentosan polysulfate, and chitosan, and thepolyamino acids are selected from the group consisting of gelatin,collagen, fibronectin, laminin, albumin, elastin, and active peptidedomains thereof.
 26. A macromer system according to claim 25 wherein thesolvent comprises formamide.
 27. A macromer system according to claim 26wherein the reactive moiety is selected from the group consisting ofglycidyl acrylate and acryloyl chloride.
 28. A macromer system accordingto claim 27 wherein the polymer comprises hyaluronic acid or collagen.29. A macromer system according to claim 24 wherein the initiatorscomprise polymer-pendent initiators.
 30. A macromer system according toclaim 24 wherein the macromer system further comprises a polymerizationaccelerator comprising a N-vinyl compound.
 31. An implantablecombination comprising a) an implant article selected from the groupconsisting of tissue implants and prosthetic devices providing a poroussurface, and b) a macromer system positioned upon the article andcomprising a polymerization initiator and one or more polymers havingpendent polymerizable groups.
 32. A combination according to claim 31wherein the macromer system is crosslinked to form a matrix suitable topermit continuous tissue growth through the matrix and between theimplant and the native tissue.
 33. An implanted combination within atissue site, the combination comprising a) an implant article selectedfrom the group consisting of tissue implants and prosthetic devicesproviding a porous surface, and b) a crosslinked matrix positionedbetween the article and the tissue site, the matrix prepared bycrosslinking a macromer system comprising a polymerization initiator andone or more polymers having pendent polymerizable groups, wherein thecombination is positioned within and/or in apposition to a tissue site.34. An implanted combination within a tissue site, the combinationcomprising a) an implant article selected from the group consisting oftissue implants and prosthetic devices providing a porous surface, b) acrosslinked matrix positioned between the article and the tissue site,the matrix prepared by crosslinking a macromer system comprising apolymerization initiator and one or more polymers having pendentpolymerizable groups, wherein the combination is positioned withinand/or in apposition to a tissue site, and wherein continuous tissueingrowth is present through the matrix and between the tissue site andthe implant article.
 35. A crosslinkable macromer system comprising oneor more polymers providing pendent polymerizable and pendent initiatorgroups wherein the system is adapted to be polymerized in order to forma matrix suitable for in vivo application, and wherein either: (a) thepolymerizable groups and initator group(s) are pendent on differentpolymers and the initiator groups are independently selected from thegroup consisting of long wave ultraviolet activatable molecules selectedfrom the group consisting of benzophenone, thioxanthones, and benzoinethers; visible light activatable molecules selected from the groupconsisting of ethyl eosin, eosin Y, rose bengal, camphorquinone anderythrosin; and thermally activatable molecules selected from the groupconsisting of 4,4′ azobis(4-cyanopentanoic) acid, and2,2-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride, and benzoylperoxide; and the pendent polymerizable groups are selected from thegroup consisting of vinyl groups, acrylate groups, methacrylate groups,ethacrylate groups, 2-phenyl acrylate groups, acrylamide groups,methacrylamide groups, itaconate groups, and styrene groups, or (b) thepolymerizable groups and the initiator group(s) are pendent on the samepolymer and the initiator groups are independently selected from thegroup consisting of long wave ultraviolet activatable molecules selectedfrom the group consisting of thioxanthones, and benzoin ethers; visiblelight activatable molecules selected from the group consisting of ethyleosin, eosin Y, rose bengal, camphorquinone and erythrosin; andthermally activatable molecules selected from the group consisting of4,4′ azobis(4-cyanopentanoic) acid, and 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and benzoyl peroxide; and the pendentpolymerizable groups are selected from the group consisting of vinylgroups, acrylate groups, methacrylate groups, ethacrylate groups,2-phenyl acrylate groups, acrylamide groups, methacrylamide groups,itaconate groups, and styrene groups; or (c) the polymerizable groupsand the initiator group(s) are pendent on the same polymer and theinitiator groups are independently selected from the group consisting oflong wave ultraviolet activatable molecules selected from the groupconsisting of benzophenone, thioxanthones, and benzoin ethers; visiblelight activatable molecules selected from the group consisting of ethyleosin, eosin Y, rose bengal, camphorquinone and erythrosin; andthermally activatable molecules selected from the group consisting of4,4′ azobis(4-cyanopentanoic) acid, and 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and benzoyl peroxide; and the pendentpolymerizable groups are selected from the group consisting of acrylategroups, methacrylate groups, ethacrylate groups, 2-phenyl acrylategroups, acrylamide groups, methacrylamide groups, itaconate groups, andstyrene groups, wherein the macromer system further comprises apolymerization accelerator comprising a N-vinyl compound.